1. Happening or arising without apparent external cause; self-generated.
2. Arising from a natural inclination or impulse and not from external incitement or constraint.
3. Unconstrained and unstudied in manner or behavior.
4. Growing without cultivation or human labor.
[From Late Latin spontneus, of ones own accord, from Latin sponte; see (s)pen- in Indo-European roots.]
Synonyms: spontaneous, impulsive, instinctive, involuntary, automatic These adjectives mean acting, reacting, or happening without apparent forethought or prompting. Spontaneous applies to what arises naturally rather than resulting from external constraint or stimulus: The highest and best form of efficiency is the spontaneous cooperation of a free people (Woodrow Wilson). Impulsive refers to the operation of a sudden urge or feeling not governed by reason: Buying a car was an impulsive act that he immediately regretted. Instinctive implies behavior that is a natural consequence of membership in a species. The term also applies to what reflects or comes about as a result of a natural inclination or innate impulse: Helping people in an emergency seems as instinctive as breathing. Involuntary refers to what is not subject to the control of the will: People drew in their breath with involuntary surprise and suspense (Harriet Beecher Stowe). Automatic implies an unvarying mechanical response or reaction: She accepted the subpoena with an automatic thank you.
spontaneous /spntenis/ adj.1 not planned, full of feeling: spontaneous laughter at a clown2 happening in a natural way, not practiced or rehearsed: the spontaneous flow of jazz music3 happening without being caused by s.t. outside: a spontaneous fire-adv. spontaneously.